Mixer circuit



July 19, 1955 A BE JR" ET AL 2,713,634

MIXER CIRCUIT Filed April 10, 1952 INVENTORS RUYHBEERSJR. WILLIHM LEENSEL [4& ATTORNEY MIXER CIRCUIT Roy A. Beers, Sin, Audubon, N. 1., and William L. Gensel, Drexel Hill, Pa., assignors to Radio Corporation of America, a corporation of Delaware Application April 10, 1952, Serial No. 281,584 4 Claims. (Cl. 250-20) This invention relates to a mixer circuit, and more particularly to a combined oscillator-doubler-mixer circuit.

Although not limited thereto, this invention is particularly useful in the receiver portion of a mobile transmitter-receiver, for converting mediate frequency (I. F.) to a quency. In such mobile equipment, it is highly advantageous to reduce as much as possible the number of tubes and circuit components utilized, in order to reduce the total weight and cost of the equipment.

Accordingly, an object of this invention is to devise an oscillator-mlxer circuit which uses fewer components and tubes than those of the prior art ordinarily use.

Another object is to provide a novel oscillator-multiplier-mixer circuit utilizing only a single tube.

A further object is to devise a novel doubler-mixer circuit in which no extra tuned circuit is necessary in order to effect the doubling function.

Still another object is to device an improved oscillatordoubler-mixer circuit which is rather simple in construction yet highly effective in operation.

The objects of this invention are accomplished, briefly, in the following manner: A single twin-triode vacuum tube is utilized in this invention, the first triode section acting as the oscillator-multiplier and the second triode section as the mixer. The three electrodes of the first triode section are connected as a crystal-controlled Colpitts oscillator. Frequency multiplication fected in the anode circuit of this first section through of which the signal to be heterodyned down in frequency is applied. The multiplied (doubled) frequency and the signal to be heterodyned down are then both fed to the grid of the second triode section, and mixing of these two frequencies takes place in this section, the changed frequency being taken from the anode of this second triode section.

The foregoing and other objects of the invention will be best understood from the following description of an exemplification thereof, reference being had to the accompanying drawing, wherein the single figure is a schematic representation of a circuit arrangement according to this invention.

Now referring to the drawing, the evacuated electron discharge device 1 is the single tube used as an oscillatordoubler-mixer according to this invention. Tube 1 is of the twin-triode type and may be type 12AU7 or 12AT7, having two entirely independent triode sections, the first of which consists of anode 2, grid or control electrode 3 and cathode 4, and the second of which consists of anode 5, grid or control electrode 6 and cathode 7. A piezoelectric crystal 8 is connected between grid 3 and ground, a resistor 9 being connected across this crystal, or also between grid 3 and ground. Cathode 4 is connected through a parallel RC network, consisting of a resistor 10 and a capacitor 11, to ground or one nited States Patent 2,713,634 Patented July 19, 1955 electrode of crystal 8. The interelectrode capacitance between grid 3 and cathode 4, and the capacitor 11 from cathode 4 to ground, provide a capacitive voltage divider across crystal 8 (which can be considered a tuned circuit), and the intermediate the anode 2 through a resistor 12 to the positive terminal (+210 v.) of a source of unidirectional potential.

The tube elements 24 with the associated circuit, provide a crystal-controlled Colpitts oscillator. In order to complete the oscillatory circuit, anode 2 is coupled to ground (the side of tuned circuit crystal 8 opposite to This latter coupling is made from pedance at the crystal frequency, which as an example may be eleven megacycles. Transformer secondary 14 is tuned (by means of capacitor 16)) to nearly twice the crystalfrequency, and as an example such secondary may be tuned to twenty megacycles. Since secondary 2-4 is essentially at ground potential at the crystal frequency, and may be considered connected to the grounded side of crystal 8. As a result, the triode section 24 acts as a crystal-controlled Colpitts oscillator, producing oscillations which appear at anode 2. Due to the fact that the equivalent resonant circuit 8 is connected essentially between grid 3 and cathode 4, the oscillator elfectively produces oscillations between such grid and cathode, so that the frequency of the oscillator is not affected by any oscillator.

The transformer 15 is tuned to the high intermediate frequency (I. F.=2O mc.) of the input signal which is to be beaten down or heterodyned down in frequency by the mixer circuit of the invention. The input signal is representative of energy received on a radio receiver, reduced in frequency in a suitable mixer or detector, and then applied to winding 17 of transformer 15. This high I. F. is sufficiently close to the harmonic (which in the example chosen would be 22 mo.) to provide sufficient impedance at the 22 mc.

tuning of the anode circuit of the to the anode 2 of which the tuned transformer secondary 14 is connected. Thus, the second harmonic of the crystal oscillator frequency (22 mc.) appears in the secondary circuit 14 of transformer 15.

It may therefore be seen that one triode half or section (elements 2, 3 and 4) of the twin triode tube 1 acts as a heterodyne oscillator-frequency doubler.

The high intermediate frequency (20 mc., for example) input signal to the mixer of the invention is applied across the tuned primary winding 17 of transformer 15. Winding 17 is tuned by means of a parallel capacitor 18.

the high I. F. input or signal frequency are applied to 19 connected between the ungrounded end of winding 14 and such grid. A grid leak resistor 29 is connected between grid 6 and ground. A

tive terminal (+210 v.) of a source of unidirectional potential. A bypass capacitor 27 is connected between the anode end of resistor 26 and ground, in order to keep the I. P. out of the unidirectional potential source.

The second triode half or section (elements 5, 6 and 7) of the twin triode tube 1 acts as a mixer. The second harmonic (22 1116.) of the crystal frequency beats with the high I. F. input frequency me.) in the mixer half of tube 1 (both of these last-named frequencies being applied to grid 6 of this triode section) to give the low I. F. of 2 me. which appears in the primary winding 23 coupled to anode 5. Winding 23 is tuned to the 2 mc. difference frequency, by means of capacitor 24. One end of the secondary 28 of transformer is grounded, While the low I. F. mixer output (2 me.) is taken from the other end of said secondary. Winding 23 is tuned to the 2-mc. difference frequency, by means of a parallel capacitor 29.

Transformer secondary 14, being tuned to the high I. F. input frequency of 20 me. and therefore offering low impedance at frequencies remote therefrom, provides filtering action, in effect by-passing to ground, and preventing from getting to the mixer grid 6, the fundamental crystal frequency, or harmonic frequencies thereof other than the second. In this way, spurious responses are prevented. In addition, the transformer 15 provides an effective means of coupling the oscillator-multiplier 2, 3, 4 and also the input signal, to the mixer 5, 6, 7. Also, since the secondary 14 of this transformer is used for frequency doubling, no separate or additional tuned circuit is nessary to effect such doubling. 7

it can be seen, from the foregoing description, that only a single tube 1 is needed for the entire oscillatordoubler-rnixer function, both halves of a twin-element tube being utilized.

The following values are given but only by Way of example, for the components illustrated in the drawing. These values were actually used in a circuit built according to this invention and successfully tested.

Resistor 9 ohms. 100,000 Resistor 10 do 2,700 Resistor 12 do 47,000 Resistor 20 d0 100,000 Resistor 21 d0 2,700 Resistor 26 do 1,000 Capacitor 11 rnmfd 27 Capacitor 13 m-mfd 100 Capacitor 16 mmfd 22 Capacitor 18 mmfd 22 Capacitor 19 mmfd 33 Capacitor 22 rnfd .01 Capacitor 24 mmfd 51 Capacitor 27 mfd .01 Capacitor .29 mmfd 51 The low I. F. (2 me.) output from transformer 25 is fed to suitable low frequency conversion circuits to transform the same to an audio frequency for utilization in a transducer circuit such as a loudspeaker or headphones.

The term ground herein employed is not limited to an actual earthed connection but is deemed to include a point of zero radio frequency or fixed reference potential.

What is claimed is:

1. In a mixer circuit for a receiver, an electrode structure having a plurality of electrodes including an anode electrode, a resonant circuit intercoupling said electrodes for the generation of oscillatory energy, said energy appearing at said anode electrode, a parallel resonant circuit having substantial impedance at a selected harmonic of the frequency of said oscillatory energy but negligible impedance at said oscillatory energy frequency, means coupling one end of said last-named circuit to said anode electrode, means connecting the other end of said lastnamed circuit to ground, whereby oscillatory energy of said harmonic frequency appears in said parallel resonant circuit, means for supplying received signal energy to said parallel resonant circuit, a triode electrode structure having anode, cathode and control electrodes, means for applying the voltage across only said parallel resonant circuit to said control electrode as the sole signal input thereto, and an output circuit coupled to said last-named anode electrode.

2. In a mixer circuit for a receiver, an electrode structure having a plurality of electrodes including an anode electrode, a resonant circuit intcrcoupling said electrodes for the generation of oscillatory energy, said energy appearing at said anode electrode, a parallel resonant circuit tuned to the frequency of the received signal energy and having substantial impedance at a selected harmonic of the frequency of said oscillatory energy but negligible impedance at said oscillatory energy frequency, the received signal energy and the selected harmonic frequency being of the same order of magnitude, means coupling one end of said last-named circuit to said anode electrode, means connecting the other end of said last-named circuit to ground, whereby oscillatory energy of said harmonic frequency appears in said parallel resonant circuit, means for supplying received signal energy to said parallel resonant circuit, a triode electrode structure having anode, cathode and control electrodes, means for applying the voltage across only said parallel resonant circuit to said control electrode as the sole signal input thereto, and an output circuit coupled to said last-named anode electrode.

3. in a mixer circuit for a receiver, an electrode structure having a plurality of electrodes including an anode electrode, a resonant circuit intercoupling said electrodes for the generation of oscillatory energy, said energy appearing at said anode electrode, a transformer having a parallel tuned secondary winding and a primary winding, said tuned secondary winding having substantial impedance at a selected harmonic of the frequency of said oscillatory energy but negligible impedance at said oscillatory energy frequency, means for supplying received signal energy to said primary winding, means coupling one end of said secondary winding to said anode electrode, means connecting the other end of said secondary w nding to ground, whereby oscillatory energy of said harmonic frequency appears in said secondary winding, a riode electrode structure having anode, cathode and conrol electrodes, means for applying the voltage across only ,aid secondary winding to said control electrode as the sole signal input thereto, and an output circuit coupled to said last-named anode electrode.

4. in a mixer circuit for a receiver, a triode electrode structure having a plurality of electrodes including an anode electrode, a resonant circuit intercoupling said electrodes for the generation of oscillatory energy, said energy appearing at said anode electrode and said resonant circuit including a piezoelectric crystal for stabilizing the frequency of said energy, a transformer having a secondary which is parallel tuned to the frequency of the received signal energy, said secondary having substantial im pedance at a selected harmonic of the frequency of said oscillatory energy but negligible impedance at said oscillatory energy frequency and the received signal energy frequency and the selected harmonic frequency being of the same order of magnitude, whereby oscillatory energy of said harmonic frequency appears in said secondary, means for supplying the received signal energy to the primary of said transformer, means coupling one end of said secondary to said anode electrode, means coupling the other end of said secondary to ground, a triode electrode structure having anode, cathode and control electrodes. means for applying the voltage developed across only said secondary to said control electrode as the sole signal input thereto, and an output circuit coupled to said last-named anode electrode.

(References on, following page) References Cited in the file of this patent 2,342,986 UNITED STATES PATENTS 1,793,959 Powell Feb. 24, 1931 1,828,094 Andi-ewes Oct. 20, 1931 2,091,546 Hruska Aug. 31, 1937 504,560 2,186,980 Lowell Ian. 16, 1940 505,124

6 Van den Bosch Feb. 29, 1944 Goldberg July 31, 1951 Dammers Nov. 4, 1952 FOREIGN PATENTS Great Britain Apr. 24, 1939 Great Britain May 5, 1939 

